The present invention relates to a container closure comprising a peripheral section adapted to be attached to a peripheral edge of an opening of a container body, a panel section surrounding by the peripheral section, and a score section formed on the periphery of the panel section for providing a weaken region and to a method for manufacturing such container closure.
It is common to store beverage and food in a container like a can and close the container tightly with a sealing closure for preservation or sales display at a shop front. A closure for this type of container is structured to have a score line for breaking the closure so that the container is opened by pulling a pulling tab provided to the closure to thereby break the closure along the score line.
Conventional container closure provided with this type of pulling tab may include those which are totally or substantially formed of a metallic material and those which are formed of a plastic material by injection molding. The closure using plastic material generally has a gas barrier layer whose major component is aluminum foil which is covered by layers of a plastic material formed by injection-molding on either or both sides of the gas barrier layer. At the peripheral section formed is a rim to be attached to a peripheral edge portion of the opening of the container body.
The Japanese Patent Publication No. 64-10170 describes a container closure having a peripheral section attached to a peripheral edge of an opening of a container body and a panel section covering an area surrounded by the peripheral section, on the opposite side of a surface of a multi-layer substrate, where heat-fusible plastic layers are formed on two or one side of a gas barrier material, the surface coupling with the opening of the container body, and manufacturing method thereof. In manufacturing method for the container closure, described in the above publication, one or more gate is used respectively for forming the peripheral section and the panel section. Since a score section of the container closure described in the publication is composed only of the multi-layer substrate, it may be easy for the closure to be broken but has problem on low drop-resistant strength. For forming the closure, one or more, gate is necessary respectively for the peripheral section and the panel section. That is, two or more gates have to be provided for forming one closure.
In such a mold subjecting to two or more gates, it is necessary to provide two or more manifolds and whereby to provide excessive area for arranging the manifolds to prevent from interference of each manifold when the mold for a closure having 80 mm or less in nominal inner diameter (307 xe2x88x85 or less in nominal diameter). Thus, when the mold was installed in restricted space, available number of molds attached would be constrained so that problem on lower productivity would be caused.
It is therefore an object of the present invention to provide a container closure that is easy to manufacture and has excellent drop-resistant strength.
Another object of the present invention is to provide a method for manufacturing such container closure.
The present invention provides a container closure comprising, a substrate having adequate property for retaining an object which is enclosed in a container, a peripheral section formed on the periphery area of the container closure on the opposite side of a side where the substrate is attached to a container body, a panel section covering an area of the substrate surrounding by the peripheral section on the same side where the peripheral section is provided, and a score section formed between the peripheral portion and the panel section to provide a weakened region, the peripheral section and the panel section is a plastic layer formed with the same heat-fusible plastic on the substrate, substantial area of the score section constructed of the substrate, characterized in that the thin layer formed on at least a part of the substrate of the score section with the heat-fusible plastic which connects the peripheral section and the panel section.
In one embodiment of the present invention, a pulling tab is attached to the panel section to separate the panel section from the peripheral section along the score line by pulling the pulling tab off. On the plastic material layer of the panel section, a projection extending laterally with respect to the pulling tab at a position adjacent to the front end portion of the pulling tab can be integrally formed with plastic material. The pulling tab may further include a puncture portion for causing the panel section to be broken along the score section when the pulling tab is pulled off to the panel section.
A thin layer is provided on circumference or a part of the score section. For forming the tab, the panel section and the peripheral section by an injection-molding machine having one gate, it needs to have a connecting portion where the panel section and the peripheral section are connected with each other. The thin layer is provided from this point of view and may be formed on entire circumference, half round, or several areas with desired width of the score section. Several areas of the thin layer may also be formed in bridge-shape.
Thickness of the thin layer is generally desirable to be as less as possible for easy opening of the container, but excessive reduction of the thickness disturbs the flow of plastic through the connecting portion. Though flowability of plastic and formability can be improved by increasing the thickness, excessive increase disturbs to the easy opening. Thickness of the thin layer is generally desirable to be set in 80-150 xcexcm in consideration of the easy opening. For maintaining the easy opening, thickness of the thin layer is desirable to be decreased. Considering better flowability of plastic through the thin layer in molding process, plastic having high flowability, preferably having M.R.F (Melt Flow Rate) of 30 or more is desirable to be used.
The present invention further provides a method for forming the above container closure by molding plastic material. In this method, a metal mold is first prepared, the mold comprising, a peripheral recess for forming the peripheral section, a center recess for forming the panel section, a connection recess for forming the thin layer which connects at least an area between both the recesses, and an injection gate for injecting plastic to either of the peripheral recess and the center recess. The present method provides steps, the steps comprising, positioning the substrate along a molding surface of the mold, closing the mold, injecting molten heat-fusible plastic on the substrate through the injection gate so that the plastic may flow from one of the peripheral recess and center recess to another of the recesses through the connection recess to form the thin layer between the peripheral section and the panel section of the container closure.
In a method for forming the container closure according to one embodiment of the present invention, all of the panel section, the pulling tab and the peripheral section can be formed only by one gate disposed in either of the center recess for forming the panel section and a recess for forming the pulling tab disposed in the center recess. Thus, one resultant closure can be obtained only one manifold so that interference of each manifold in case of two or more gates can be avoided. Accordingly, since the manifold doesn""t occupy its space more than necessary so that adequate number of molds can be attached to achieve lower plant investment and higher productivity.